The present invention relates to a method for determining copper content in a direct process contact mass. More particularly, the present invention relates to determining the eta phase copper content in a direct process contact mass.
Rochow, U.S. Pat. No. 2,380,995 discloses preparing a mixture of alkylhalosilanes by a direct reaction between powdered silicon and an alkylhalide in the presence of a copper-silicon alloy. This reaction is commonly referred to as the xe2x80x9cdirect methodxe2x80x9d or xe2x80x9cdirect process.xe2x80x9d The reaction can be summarized as follows: 
where Me is methyl.
In addition to the above methylchlorosilanes, xe2x80x9cresiduexe2x80x9d is also formed during the production of methylchlorosilane crude. Residue means products in the methylchlorosilane crude having a boiling point greater than about 70xc2x0 C., at atmospheric pressure. Residue consists of materials such as disilanes for example, symmetrical 1,1,2,2-tetrachlorodimethyldisilane; 1,1,2-trichlorotrimethyIdisilane; disiloxanes; disilmethylenes; and other higher boiling species for example, trisilanes; trisiloxanes; trisilmethylenes; etc.
As shown, the alkylhalosilanes formed by the direct reaction include dimethyldichlorosilane referred to as xe2x80x9cDxe2x80x9d or xe2x80x9cDixe2x80x9d and methyltrichlorosilane, referred to as xe2x80x9cTxe2x80x9d or xe2x80x9cTrixe2x80x9d. These are the major products of the reaction, which typically produces dimethyldichlorosilane in a range between about 80% and about 88% and methyltrichlorosilane in a range between about 5% and about 10%. Dimethyldichlorosilane has the highest commercial interest. A T/D ratio is the weight ratio of methyltrichlorosilane to dimethyldichlorosilane in the crude methylchlorosilane reaction product. An increase in the T/D ratio indicates that there is a decrease in the production of the preferred dimethyldichlorosilane. Hence, the T/D product ratio is the object of numerous improvements to the direct reaction.
Gilliam, U.S. Pat. No. 2,464,033 discloses using zinc in combination with copper catalyst as a promoter to achieve a higher selectivity of dimethyldichlorosilane. Gilliam discloses that a proportion in a range between about 2% and about 50% by weight of copper in elemental form or as the halide or oxide, and preferably 5 to 20% and zinc in a range between about 0.03% and about 0.75% by weight in the form of zinc halide, zinc oxide, or zinc metal, or mixture thereof, where the weights of copper and zinc are based on the weight of silicon, can be used as a promoter for making dialkyl substituted dihalogenosilanes, such as dimethyldichlorosilane in the direct reaction between silicon powder and methyl chloride.
Radosavlyevich et al., Influence of Some Admixtures on the Activity of Contact Masses for Direct Synthesis of Methylchlorosilanes, INSTITUTE OF INORGANIC CHEMISTRY, Belgrade, Yugoslavia, (1965) discloses that micro quantities of silver added to contact masses resulting from the reaction of powdered silicon and methyl chloride in the presence of cuprous chloride decreases the yield of methylchlorosilanes, while tin and calcium chloride increase the rate of formation of methylchlorosilanes.
Rong et al., Aluminum as Promoter for the Direct Process to Methylchlorosilanes, Silicon for the Chemical Industry III, J. KR. TUSET EDS. 199 (Trondheim, Norway, 1996) discloses adding solid aluminum compounds to improve reactivity and selectivity of the direct process. Ward et al., U.S. Pat No. 4,500,724 discloses that tin and zinc are important in improving the direct method and can be controlled to provide improved alkylhalosilane product selectivity.
Copper silicide, Cu3Si (eta phase), is a preferred form of copper and silicon in the contact mass of a direct process to provide improved selectivity. In general, factors that improve selectivity also increase the proportion of the Cu3Si form in the copper/silicon contact mass. Many of the factors that can improve the direct process and correspondingly the proportion of Cu3Si are known. However, an extent of improvement brought about by factors, either singly or in combinations of factors is not known. Methods are constantly being sought to monitor a direct process to determine the Cu3Si form of copper and silicon in the contact mass so that the combinations of factors can be determined that maximize selectivity of a direct process.
The present invention permits monitoring of the direct process so that processing factors can be optimized for improved selectivity. According to the present invention, the proportion of Cu3Si in a contact mass can be determined by treating the mass with an inorganic ammonium salt composition, which selectively dissolves all forms of copper including free copper in deference to Cu3Si, which is not dissolved. The invention relates to a method of determining a Cu3Si content of a copper and silicon contact mass, comprising determining an initial copper content of the contact mass, treating the contact mass with inorganic ammonium salt composition to extract copper in a molecular form other than Cu3Si and subtracting extracted copper from the initial copper content.
In another embodiment, an alkylhalosilane is made by forming a copper and silicon contact mass, treating the contact mass with an inorganic ammonium salt composition to extract copper in a form other than Cu3Si and effecting reaction of an alkyl halide in the presence of the treated contact mass to produce alkylhalosilane.
In still another embodiment, the present invention relates to an alkylhalosilane reaction vessel containing Cu3Si substantially free from other forms of copper. xe2x80x9cSubstantially free from other forms of copperxe2x80x9d as used herein refers to Cu3Si present in an amount greater than about 90% by weight of the total amount of copper.